The invention relates to a holding device comprising an individual tooth replacement or basic framework model produced by dental technology and means for clamping the device in a measuring machine. The invention also relates to a method for positioning a model of this type in a holding device.
Tooth replacement or basic framework models, hereinafter called preparation models, have different shapes and sizes. They consist primarily of modelling wax or modelling plastics material. It is necessary to measure them to work the tooth replacement or the basic framework for tooth restorations from an industrially preproduced blank with the aid of manual, semi-automatic or automatic production apparatus. Tooth restorations are, for example, tooth crowns and bridges comprising a load-bearing basic framework on which further layers made of porcelain, ceramic or plastics material are applied. Basic frameworks are individual productions and are usually produced once individually for a patient in the normal procedure. It is similar for a tooth replacement which, apart from the basic framework, already contains layers made of porcelain, ceramic or plastics material.
Preparation models which are produced individually for a patient vary with respect to length, width and positioning of the individual parts. They can be differently bent both in the cranio-caudal and bucco-palatinal direction according to the anatomical conditions. Basic frameworks consist of a small cap for tooth crowns. These have an inside and an outside, which may be completely or partially coated, forming the cavity. The inside of the cavity fits precisely on the natural tooth prepared by the dentist, the tooth stump or else on an artificial tooth stump, for example an implant. Tooth bridges consist of a plurality of connected members of which at least one is designed as a small cap, while the others can be designed as bridge and/or exstress members. Cavities per se have to be free of undercuts in alignment to the other cavities, so the tooth restoration can be placed as a whole onto the prepared teeth.
Measuring a preparation model offers an important advantage compared to measuring a plaster model, in that the dental technician can design and assess the physical model as previously with his familiar aids. With objects shaped as complexly as this, visual and touch impressions are very important. Supplementing the measuring data on the computer does not offer the dental technician the same familiar impressions and is therefore much more challenging to his powers of abstraction and imagination. Producing preparation models from wax, plastics material or other easily processible materials is known in dental technology as general expert knowledge and guide to handling and therefore prior art. This technology is also used, in particular for moulding methods, for example in the widespread casting and hot press technology. Measuring such preparation models requires them to be fixed in a measuring machine, preferably on its rotary shaft.
Preparation models, in other words in particular models for basic frameworks for tooth crowns and bridges, are already frequently used in dental technology. They are formed by the casting method and hot press method, for example a negative mould of the basic frame being developed in a fireproof mould. The negative mould represents a cavity which is then filled with dental material. These methods are not considered here.
Other methods measure the preparation model digitally, or they transfer the mould of the preparation model during measurements, by means of mechanical coupling, to the machining tools. All methods of this type need a suitable holding device for the preparation model.
DE,C1 19916148 describes a universal holder for holding operating means, inter alia models in tooth technology. Owing to the combination of rigid and formable parts in the holder any adjustment angles can be achieved. The formable part is designed like a cushion and has a reversibly formable outer skin, which is filled with granules. This allows a spatial, single-handed orientation of workpieces during machining, in particular during casting of dental impressions and dental technology models.
An automatic machine tool for measuring preparation models and producing basic frameworks, in particular for tooth crowns and/or tooth bridges of precise three-dimensional design, is described in PCT/CH00/00623. This machine tool comprises a machine frame or a machine housing, with a rotary shaft for a support for the blank on one side and a support for the preparation model on the other side, at least one machining unit, at least one measuring or digitalising unit and an electronic computing and control unit for all the drive members. A movement unit with three axes of translation in the x, y and z directions is formed for machining unit(s) and measuring unit(s). The digitalisation of the preparation model and machining of the blank are carried out on the same machine tool, at different times. Prior to machining the blank the machining paths for the blank are calculated from the determined and stored digitalisation data, a preset, material-specific scale factor and the tool geometry.
With a view to the prior art it can be established that no convincing specific holding device for dental preparation models is known; there are merely rudimentary aid solutions.
The object of the present invention is to provide a holding device of the type mentioned at the outset, in which the individuality of the preparation model and its complex form is particularly taken into account. The preparation model must be fixable free of undercuts. Moreover, a method for positioning a preparation model in its holding device is to be provided.